DESCRIPTION: (Adapted from the Applicant's Abstract.) The projects in this application test ideas about the way that human listeners localize sounds. Particularly, these projects test the idea that sources in the median vertical plan (MVP) are localized on the basis of spectral cues such as direction bands. An elementary test is to study MVP localization using signals of different spectral distribution to find the kinds of linear distortions that cause listeners to make errors. Also, the idea of spectrally-based localization has implications for the precedence effect: In sharp contrast to localization in the horizontal plane, localization based upon direction bands should show no precedence effect for ongoing broad-band noise. Again, unlike azimuthal localization, spectrally-based localization should not be changed if reflections from a ceiling are substituted for reflections from a floor. The time constants for the precedence effect for spectrally-based localization can be measured in several different ways, and if the fundamental ideas are correct then these measurements should agree. A model of localization based upon direction bands also requires rules about how cues from different spectral regions are combined. In some cases different spectral bands, heard simultaneously, are perceived as separate sources. In other cases, the bands are combined to create a fused source image. It is also important to know how information from vertical localization is combined with information on localization in the horizontal plane to create an image in three dimensions. Experiments proposed in this application address all those predictions and questions. Other experiments, on localization in the horizontal plane, are designed to solve measurement problems, specifically understanding the effects on localization and on source identification that occur when the range of sources and the range of response options is